1. Preheat the Griddle: Heat your griddle or skillet over medium heat, getting it nice and hot for the perfect sear on your sandwiches.

2. Mix the Brisket and BBQ Sauce: In a bowl, combine the shredded brisket with the BBQ sauce, making sure the meat is evenly coated.

3. Caramelize the Onions: In a separate pan, sauté the onions over medium-low heat, stirring occasionally, until they develop a rich, golden-brown color and sweet, caramelized flavor.

4. Prepare the Toppings: While the onions are caramelizing, take the time to prepare the other toppings, such as chopping the bacon and slicing the jalapeños (if using).

5. Assemble the Sandwiches: Spread a thin layer of butter on one side of each slice of sourdough bread. On the unbuttered side, layer the cheddar cheese, the BBQ brisket mixture, the chopped bacon, the caramelized onions, and the jalapeños (if using). Top with another slice of bread, buttered side up.

6. Grill the Sandwiches: Place the assembled sandwiches on the preheated griddle and cook for 4-5 minutes per side, or until the bread is golden brown and the cheese is melted and oozing.